Geology/faults

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Expert: Manoharan Kothandapani alias Manoharan - 9/15/2013

Questionhow to identify faulting zone

AnswerDear Mr. Ahmed Khot
Thanks for your question and sorry for the delay as i was in field work and unable to access internet.
Fault is a planar fracture or discontinuity in a rock, across which there has been significant displacement along the fractures as a result of earth movement. There are several classifications for these and you may refer some standard text books on structural geology.
Faults and fault zones are mainly identified by following features.
Fault zone features include
Cataclasite - a fault rock which is cohesive with a poorly developed or absent planar fabric, or which is incohesive, characterised by generally angular clasts and rock fragments in a finer-grained matrix of similar composition.
Tectonic or Fault breccia - a medium- to coarse-grained cataclasite containing >30% visible fragments.
Fault gouge - an incohesive, clay-rich fine- to ultrafine-grained cataclasite, which may possess a planar fabric and containing <30% visible fragments. Rock clasts may be present
Clay smear - clay-rich fault gouge formed in sedimentary sequences containing clay-rich layers which are strongly deformed and sheared into the fault gouge.
Mylonite - a fault rock which is cohesive and characterized by a well developed planar fabric resulting from tectonic reduction of grain size, and commonly containing rounded porphyroclasts and rock fragments of similar composition to minerals in the matrix
Pseudotachylite - ultrafine-grained vitreous-looking material, usually black and flinty in appearance, occurring as thin planar veins, injection veins or as a matrix to pseudoconglomerates or breccias, which infills dilation fractures in the host rock.
Apart from these remote sensing studies using imageries can help you identification, water level variations, discontinuity in beds, soil type, vegetation variation can also possibly indicate faults.
Deep faults could be identified by seismic survey as done for oil and gas identification studies and also subsurface logs are studied for fault identification. Thus identification of fault zone throw light on identification of fault and vice-versa
Thanks,
Kothandapani Manoharan